1. Field of the Invention
The present invention relates to a variable optical attenuator for optical communications, and particularly, to a variable optical attenuator for optical communications used as an interface device of an optical communication network and configured to be easily manufactured at a reduced manufacturing cost.
2. Description of the Background Art
Recently, information-related technologies are being remarkably developed with development of high-speed communication technologies using an optical fiber that can transmit and receive a large amount of information. Particularly, the transfer speed of multimedia information including various kinds of data such as moving images, audio signals, character signals and the like increases, an interactive communication environment is established and the number of users explosively increases. Thus, a communication network using an existing copper line for transmission is not sufficient to cope with such development. For this reason, a communication network using an optical signal having a high carrier frequency is being considered as the alternative.
In the optical communication network using light as an information transfer signal, an optical connector module, instead of a logic integrated circuit used in the communication network using an existing copper transmission line, is used as an interface for connecting a user with a repeater or a common carrier.
The optical connector module, which is a data interface for such an optical communication network includes: a transmission line made of an optical fiber, an optical reception module used to receive an optical signal, an optical transmission module used to transmit an optical signal, and an optical repeater. However, the optical connector module requires precise processing and assembly, which makes its manufacturing cost expensive.
Also, the optical connector module should satisfy the following requirements: small power consumption, lightness and smallness for easy handling, and good mechanical/optical characteristics. However, it is not easy to manufacture an optical connector module that meets all the requirements.
Meanwhile, a variable optical attenuator, one of parts for optical fiber communication, is increasingly drawing attention. This is because each device is driven by a wide range of optical output from high level output signal, which is outputted from a transmitter, an amplifier or the like, to a low level signal inputted to a receiver. For example, in order to attenuate the optical output of a light receiving part, a fixed optical attenuator is used in a short distance optical fiber transport network. Also, a variable optical attenuator for controlling the size of an optical signal with respect to multi-channels in a WDM (wavelength-division-multiplex) optical network is in development.
As an optical switch including the optical attenuator, there are a bulk optomechanical switch, a liquid crystal switch, a lithium niobate switch, a thermal optical switch using a waveguide and the like. However, although there are various types of switches, there is a limit to the manufacturing of a switch which is ultralight and can maintain high mechanical/optical characteristics while consuming a small amount of power.
To overcome such limits, researches on a variable optical attenuator and various precision parts for optical fiber communication using a semiconductor manufacturing process and a micromachining technique are actively ongoing.
FIGS. 1 to 3 illustrate a conventional optical attenuator for optical communications using a microspherical lens. FIG. 1 is a perspective view illustrating a structure of the conventional variable optical attenuator, FIG. 2 is a perspective view illustrating a structure of a collimating lens system of FIG. 1, and FIG. 3 is a schematic view illustrating an operational principle of the collimating lens system of FIG. 2.
As shown, the conventional optical attenuator for optical communications includes: a first collimating lens system 10 collimating and transmitting an input optical signal 5a; a reflector 20 installed on the substrate so as to be rotated to change a direction of the optical signal 5b outputted from the first collimating lens system 10 by a certain angle (α); and a second collimating lens system 30 installed on the substrate at a certain angle (α) from the first collimating lens system 10 with respect to an optical signal 5b that is incident on the reflector 20, for collimating and outputting an optical signal 5c reflected by the reflector 20.
The first and second collimating lens systems 10 and 30 and the reflector 20 are installed in receiving grooves 41 and 42 patterned on a substrate 40 of a silicon material.
As shown in FIG. 2, the first collimating lens system 10 includes: an optical fiber 11 transmitting an optical signal 5a; and a microspherical lens 12 separated from one end of the optical fiber 11 at a predetermined distance so as to collimate the optical signal 5a having passed through the optical fiber 11. Likewise, the second collimating lens system 30 includes: a microspherical lens 32 for collimating an optical signal 5c whose direction has been changed by the reflector 20; and an optical fiber 31 separated from the microspherical lens 32 at a predetermined distance and transmitting the optical signal 5c which has been collimated while passing through the microspherical lens 32.
As shown in FIG. 3, an optical signal 5a′, which is an optical signal 5a that has not reached the spherical lens 12, has not been collimated yet. While passing through the spherical lens 12, the optical signal 5a′ is collimated in horizontal and perpendicular directions to the silicon substrate 40, thereby increasing an optical density of the optical signal 5. Therefore, the optical efficiency can be improved.
The operation of the conventional optical attenuator for the optical communications will now be described in detail.
The optical signal 5a is collimated in horizontal and vertical directions to the silicon substrate 40 while passing through the first collimating lens system 10, and the collimated optical signal 5b undergoes a change in its advancing direction by the reflector 20 by a predetermined angle of reflection. The optical signal 5c whose advancing direction has been changed by the reflector 20 penetrates the spherical lens 32 of the second collimating lens system 30 and the optical fiber 31 and then is outputted. Here, the reflector 20 is configured to be rotated to change the reflection angle (α) minutely depending on its rotation. Also, the reflector 20 controls the optical signal such that only part of the reflected optical signal 5c is incident on the second collimating lens system 30. In such a manner, the intensity of the outputted optical signal 5d, namely, the quantity of light, is controlled.
However, in the conventional optical attenuator for optical communications, the first and second collimating lenses are installed on the substrate at a certain distance corresponding to a reflection angle, which may excessively increase its size. Thus, since the entire size of a system is increased, it is difficult for the system to satisfy the requirements of lightness and smallness.
Also, since the microspherical lens that is expensive and has a diameter of less than 1 mm is used to collimate an optical signal, a manufacturing cost is increased.
Furthermore, since a collimating lens system including the microspherical lens should be aligned on a silicon substrate after the silicon substrate is processed, an alignment error in assembly increasingly occurs.